1. Field of the Invention
This invention relates to electrostatographic reproduction apparatus which reproduce original documents, and more particularly to methods and mechanisms in such reproduction apparatus for determining the size of an original document being reproduced.
2. Background Art
Electrostatographic reproduction apparatus, such as copiers, are well known for producing, on selected substrates or copy sheets, copies of original images being carried on original documents. It is common to provide in each such reproduction apparatus a transparent platen on which to position each such document, and a white colored document cover for placing over such document to form a background surface for the document. It is also common in such reproduction apparatus to provide two or three supply sources for two or three different sizes of copy sheets from which to select when making copies as above, as well as, means for magnifying or reducing the original images on the original documents being reproduced or copied in order to achieve a desired fit on the selected size of sheet.
In order to automatically determine which particular size of copy sheet to select, or in order to automatically determine a desired degree of image magnification or reduction for a selected size of copy sheet, it is also known in the art to provide a device in the reproduction apparatus for detecting or determining the size of the original document to be reproduced. For example, in U.S. Pat. No. 4,511,246, issued Apr. 16, 1985 to Nishiyama, a document size detecting emitting elements, a pivotable light reflecting means, and light receiving elements which produce size related signals for use by a control circuit responsively to the positioning of a document between the light-emitting elements and such light-receiving elements.
In U.S. Pat. No. 4,873,550, issued Oct. 10, 1989 to Watanabe, means for sensing the size of an original document are disclosed and include a platen reference point, a document size sensor and a lens that is displaced relative to an optics assembly depending on the size of the document.
In U.S. Pat. No. 4,978,992, issued Dec. 18, 1990 to Kusumoto et al, a document size detecting apparatus is disclosed and comprises a platen, a light source, a movable scanner, a scanner reference position sensor, and means for measuring the movement of the scanner in counts. Changes in the intensity of reflected light from the platen, caused by the presence of a document, is detected by a sensor relative to a reference intensity. Points of such changes as measured in counts are used to determine document size.
In U.S. Pat. No. 5,036,354, issued Jul. 30, 1991 to Miyamoto, a document size detection device is disclosed and comprises a light-emitting unit, a document cover that has a first area for reflecting light and a second area for transmitting light, and a document presence sensor in the second area. The document sensor includes light-emitting elements and light receiving elements.
In U.S. Pat. No. 5,072,259, issued Dec. 10, 1991 to Ikeda, a document size detecting system is disclosed and includes photosensors and a document detection lamp. In U.S. Pat. No. 5,081,489 issued Jan. 14, 1992 to Ishikawa et al., a sheet size detecting system is disclosed as part of an automatic document feeder which moves documents seriatim to be reproduced. The size detecting system comprises photosensors and a timing means for counting pulses to measure the movement and hence size of a document being moved.
It should be noted, however, that besides coming in various sizes, document materials which carry original images also often come in various colors, including white. Since document covers on electrostatographic reproduction apparatus are commonly white or of a light color, there ordinarily is no reflective or optically scannable difference between a background surface formed by such a white document cover and a white or light color document material. Yet, such a white document cover is necessary in such reproduction apparatus particularly for reproducing images that are carried on a transparency material. As a consequence of these difficulties, prior art document size detecting devices or systems are each obviously limited, or have had to add costly proximity or photo sensors, even in reproduction apparatus having optical scanners for other uses therein.